In the past, many automotive instrument panels were fabricated from a metal stamping which was polished and then painted. In an effort to improve vehicle occupant safety in crash situations, padding was added to the side of the dashboard that faced towards the vehicle's interior. To lower manufacturing costs and also to lower vehicular weight, padded metal dashboards were replaced with composite dashboards.
Composite instrument panels have a preformed structural member. The structural member is typically fabricated from a rigid plastic material or a wood fiber compound. A foam polymeric material covers the preform to provide for cushioning. Placed on top of the foam polymeric material is a preformed polymeric multiform skin membrane, which typically has an outer surface to simulate a textured appearance similar to leather. To fabricate such a composite dashboard, typically the skin membrane is placed into a mold spaced away from the rigid preformed structural member. The material that provides the foam cushioning is then injected into the mold and adheres to both the preformed structure and preformed skin membrane to form a composite instrument panel.
Prior to its placement into the mold to form the composite, the skin membrane is formed in a separate molding operation. To form the skin membrane, a grained plastic sheet is heated and vacuum formed over a male mold. The formed skin is then removed and trimmed to size.
As previously stated, the preformed polymeric skin is placed within a mold cavity. Prior to the present invention, as best shown in FIGS. 1A-1C, the foam tool 9 (also referred to as the mold half) which forms the mold cavity was provided. The foam tool 9 is formed in the shape of a sharp edge 7 to provide for the instrument panel. In a similar fashion the preformed skin 11 has a sharp edge 13. Often there is a slight error, typically less than 1.5 mm. in the placement of a side surface 15 from the foam tool surface 16 of the foam tool 9. Although shown in FIG. 1A in a two-dimensional diagram, it is apparent to those skilled in the art that this mismatch can have three-dimensional characteristics in that the edge 13 can project in all three axes.
Referring to FIG. 1B when the urethane foam is injected into the mold cavity, a gap 19 can form between the foam tool surface 16 and the skin 11. In other situations, the skin 11 will not shrink the anticipated amount prior to placement within the mold cavity. Accordingly, the sharp edge 13 of the skin will not properly align with the sharp edge 7 of the foam tool. The injection pressure of the urethane foam will result in a distorted surface 23 on the finished instrument panel (FIG. 1C).
In particular, tight edges or features are prone to the aforementioned distortion. These tight edges can affect fit and appearance between the instrument panel and trim panels of the vehicle and can also affect alignment with the side window defrosters and the air conditioning registers and other parts of the instrument panel. Typically, when such failure occurs, the whole instrument panel must be scrapped. Or, to prevent the occurrence of such distortions, flexibility in the design of the instrument panel is restricted.